Developing the Application

An App Engine application responds to web requests. It does so by
calling request handlers, routines that accept
request parameters and return responses. App Engine determines which
request handler to use for a given request from the request’s URL, using a
configuration file included with the app that maps URLs to
handlers.

An app can also include static files, such as images, CSS
stylesheets, and browser JavaScript.
App Engine serves these files directly to clients in response to requests
for corresponding URLs without invoking any code. The app’s configuration
specifies which of its files are static, and which URLs to use for those
files.

The application configuration includes metadata about the app, such
as its application ID and version number. When you deploy the app to App
Engine, all of the app’s files, including the code, configuration files,
and static files, are uploaded and associated with the application ID and
version number mentioned in the configuration. An app can also have
configuration files specific to the services, such as for datastore
indexes, task queues, and scheduled tasks. These files are associated with
the app in general, not a specific version of the app.

The structure and format of the code and configuration files differ for Python apps and for Java apps, but the concepts are similar. In the next few sections, we will create the files needed for a simple application in both Python and Java, and will look at how to use the tools ...

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